risingwave_meta/barrier/
backfill_order_control.rs

1// Copyright 2025 RisingWave Labs
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7//     http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15use std::collections::{HashMap, HashSet};
16
17use risingwave_common::catalog::FragmentTypeFlag;
18
19use crate::model::{FragmentId, StreamJobFragments};
20
21/// This is the "global" `fragment_id`.
22/// The local `fragment_id` is namespaced by the `fragment_id`.
23pub type ActorId = u32;
24
25#[derive(Clone, Debug, Default)]
26pub struct BackfillNode {
27    fragment_id: FragmentId,
28    /// How many more actors need to finish,
29    /// before this fragment can finish backfilling.
30    remaining_actors: HashSet<ActorId>,
31    /// How many more dependencies need to finish,
32    /// before this fragment can be backfilled.
33    remaining_dependencies: HashSet<FragmentId>,
34    children: Vec<FragmentId>,
35}
36
37/// Actor done                   -> update `fragment_id` state
38/// Operator done                -> update downstream operator dependency
39/// Operator's dependencies done -> queue operator for backfill
40#[derive(Clone, Debug, Default)]
41pub struct BackfillOrderState {
42    // The order plan.
43    current_backfill_nodes: HashMap<FragmentId, BackfillNode>,
44    // Remaining nodes to finish
45    remaining_backfill_nodes: HashMap<FragmentId, BackfillNode>,
46    // The mapping between actors and fragment_ids
47    actor_to_fragment_id: HashMap<ActorId, FragmentId>,
48}
49
50/// Get nodes with some dependencies.
51/// These should initially be paused until their dependencies are done.
52pub fn get_nodes_with_backfill_dependencies(
53    backfill_orders: &HashMap<FragmentId, Vec<FragmentId>>,
54) -> HashSet<FragmentId> {
55    backfill_orders.values().flatten().copied().collect()
56}
57
58// constructor
59impl BackfillOrderState {
60    pub fn new(
61        backfill_orders: HashMap<FragmentId, Vec<FragmentId>>,
62        stream_job_fragments: &StreamJobFragments,
63    ) -> Self {
64        tracing::debug!(?backfill_orders, "initialize backfill order state");
65        let actor_to_fragment_id = stream_job_fragments.actor_fragment_mapping();
66
67        let mut backfill_nodes: HashMap<FragmentId, BackfillNode> = HashMap::new();
68
69        for fragment in stream_job_fragments.fragments() {
70            if fragment.fragment_type_mask.contains_any([
71                FragmentTypeFlag::StreamScan,
72                FragmentTypeFlag::SourceScan,
73                FragmentTypeFlag::LocalityProvider,
74            ]) {
75                let fragment_id = fragment.fragment_id;
76                backfill_nodes.insert(
77                    fragment_id,
78                    BackfillNode {
79                        fragment_id,
80                        remaining_actors: stream_job_fragments
81                            .fragment_actors(fragment_id)
82                            .iter()
83                            .map(|actor| actor.actor_id)
84                            .collect(),
85                        remaining_dependencies: Default::default(),
86                        children: backfill_orders
87                            .get(&fragment_id)
88                            .cloned()
89                            .unwrap_or_else(Vec::new),
90                    },
91                );
92            }
93        }
94
95        for (fragment_id, children) in backfill_orders {
96            for child in &children {
97                let child_node = backfill_nodes.get_mut(child).unwrap();
98                child_node.remaining_dependencies.insert(fragment_id);
99            }
100        }
101
102        let mut current_backfill_nodes = HashMap::new();
103        let mut remaining_backfill_nodes = HashMap::new();
104        for (fragment_id, node) in backfill_nodes {
105            if node.remaining_dependencies.is_empty() {
106                current_backfill_nodes.insert(fragment_id, node);
107            } else {
108                remaining_backfill_nodes.insert(fragment_id, node);
109            }
110        }
111
112        Self {
113            current_backfill_nodes,
114            remaining_backfill_nodes,
115            actor_to_fragment_id,
116        }
117    }
118}
119
120// state transitions
121impl BackfillOrderState {
122    pub fn finish_actor(&mut self, actor_id: ActorId) -> Vec<FragmentId> {
123        let Some(fragment_id) = self.actor_to_fragment_id.get(&actor_id) else {
124            tracing::error!(actor_id, "fragment not found for actor");
125            return vec![];
126        };
127        // NOTE(kwannoel):
128        // Backfill order are specified by the user, for instance:
129        // t1->t2 means that t1 must be backfilled before t2.
130        // However, each snapshot executor may finish ahead of time if there's no data to backfill.
131        // For instance, if t2 has no data to backfill,
132        // and t1 has a lot of data to backfill,
133        // t2's scan operator might finish immediately,
134        // and t2 will finish before t1.
135        // In such cases, we should directly update it in remaining backfill nodes instead,
136        // so we should track whether a node finished in order.
137        let (node, is_in_order) = match self.current_backfill_nodes.get_mut(fragment_id) {
138            Some(node) => (node, true),
139            None => {
140                let Some(node) = self.remaining_backfill_nodes.get_mut(fragment_id) else {
141                    tracing::error!(
142                        fragment_id,
143                        actor_id,
144                        "fragment not found in current_backfill_nodes or remaining_backfill_nodes"
145                    );
146                    return vec![];
147                };
148                (node, false)
149            }
150        };
151
152        assert!(node.remaining_actors.remove(&actor_id), "missing actor");
153        tracing::debug!(
154            actor_id,
155            remaining_actors = node.remaining_actors.len(),
156            fragment_id,
157            "finish_backfilling_actor"
158        );
159        if node.remaining_actors.is_empty() && is_in_order {
160            self.finish_fragment(*fragment_id)
161        } else {
162            vec![]
163        }
164    }
165
166    pub fn finish_fragment(&mut self, fragment_id: FragmentId) -> Vec<FragmentId> {
167        let mut newly_scheduled = vec![];
168        // Decrease the remaining_dependency_count of the children.
169        // If the remaining_dependency_count is 0, add the child to the current_backfill_nodes.
170        if let Some(node) = self.current_backfill_nodes.remove(&fragment_id) {
171            for child_id in &node.children {
172                let newly_scheduled_child_finished = {
173                    let child = self.remaining_backfill_nodes.get_mut(child_id).unwrap();
174                    assert!(
175                        child.remaining_dependencies.remove(&fragment_id),
176                        "missing dependency"
177                    );
178                    if child.remaining_dependencies.is_empty() {
179                        tracing::debug!(fragment_id = ?child_id, "schedule next backfill node");
180                        self.current_backfill_nodes
181                            .insert(child.fragment_id, child.clone());
182                        newly_scheduled.push(child.fragment_id);
183                        child.remaining_actors.is_empty()
184                    } else {
185                        false
186                    }
187                };
188                if newly_scheduled_child_finished {
189                    newly_scheduled.extend(self.finish_fragment(*child_id));
190                }
191            }
192        } else {
193            tracing::error!(fragment_id, "fragment not found in current_backfill_nodes");
194            return vec![];
195        }
196        newly_scheduled
197    }
198}
risingwave_meta/barrier/backfill_order_control.rs

risingwave_meta/barrier/
backfill_order_control.rs
